Auxiliary roll stabilizer for hydrofoil craft

ABSTRACT

In a high speed watercraft of the hydrofoil type having foil appendages extending beyond and below the perimeter of the hull of the craft, stabilizing members for decreasing the roll angle of the craft in the event of a structural failure of the foil appendages, a control malfunction, or other damage causing the craft to assume an excessive roll angle.

United States Patent Inventor Frederick N. Saxtou 10712 Rock Run Drive, Potomac, Md. 20854 Appl, No. 853,446

Filed Aug. 27, 1969 Patented Aug. 10, 1971 AUXILIARY ROLL STABILIZER FOR HYDROFOIL CRAFT 1 Claim, 3 Dnwing Figs.

118. CL 114/665 Int. Cl. B63D 1/18 Field of Sal-ch 114/665 1-1 [56] References Cited UNITED STATES PATENTS 3,139,059 6/1964 Hanford 114/665 H 3,343,513 9/1967 Bader 1 14166.5 H

Primary ExaminerAndrew H. Farrell Attorneys-L. A. Miller, 0. E. Hodges, A. Sopp and W. F.

McCarthy gle.

AUXILIARY ROLL STABILIZER FOR I-IYDROFOIL CRAFT The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION Stabilization devices for conventional surface watercraft generally consist of activated fins or vanes which project from the sides of the craft and are operated by power means within the craft in such a manner as to oppose undesired craft motion due to various natural sea state conditions.

The position and movement of the fins or vanes is determined by sensing means which are responsive to chosen functions of the crafts movement, such as roll angle or pitch angle, roll acceleration and rate of change of roll acceleration, and roll velocity.

Conventionally, the fins or vanes comprising the stabilization elements are located beyond the perimeter of the hull of the craft and in most cases are positioned directly in the water for immediate use as needed. Additionally, some prior art constructions described stabilizing members which are retracted into watertight compartments within the hull of the craft. At such times as determined by unfavorable sea conditions the retracted fins or vanes are extended into the water and are thereafter operated in the well-known manner.

However, a particular class of ships or boats, known as hydrofoil craft, has been designed to operate under certain conditions with the hull of the craft above and substantially out of contact with the water. Under such operating conditions, the craft is said to be foil-home, i.e., the craft is supported in the water only by foil appendages extending downwardly from the hull.

One of the features of a foil-borne craft, or hydrofoil, is its extreme stability when operating at high speeds in all types of 'sea state conditions.

Therefore, fins, vanes, or other stabilizing equipment of conventional design, and for the purposes as hereinbefore described, are made unnecessary.

It is known, however, that under certain adverse operating conditions excessive roll problems will occur during the foilborne phase in the operation of hydrofoil craft.

For example, in the event of foil control malfunctions, structural failures in one or more of the submerged foil members, or in the case of an autopilot failure, the hull of the craft tends to roll as it descends into the water.

Experience has indicated that the roll angle developed as the result of the operating failures hereinabove mentioned is, in almost every case, excessive and may result in serious damage to the craft. Moreover, when a roll develops, the only counteracting factor for the roll is a hull-borne righting moment which does not actually come into effect until the craft has entered the sea and the hull is actually displacing some water.

The invention is therefore primarily concerned with the safety of a hydrofoil craft. In this respect, means which are hereinafter fully described have been devised which reduce the liability of the craft to capsize or sink under certain adverse operating conditions. Such means consist of providing the craft with stabilizing planes, the effect of which is to counteract undesirable roll moments occurring while the craft is foil-borne and operating at higher speeds.

As used in this application, the term hull-bome refers to a condition wherein the craft hull is in the water and the foil appendages may be in a submerged service position beneath thehull or in an out of service retracted position. The term hull borne waterline" refers to the normal waterline of the craft as the hull rests in the water. The foil-home has been heretofore described. Foil-home waterline" refers to the waterline established by a craft while it is fully supported by the hydrofoil appendages. The term "angle of attack" is an angle measured fromthe direction of flow of a fluid. As used in this craft that will improve the operating characteristics of the craft. 3

A further object of this invention is to provide asymmetrically shaped planes on each side of the hull of a hydrofoil craft above the hull-borne waterline so that the planes produce forces tending to resist overturning of the craft if a structural failure in the foil appendages occurs.

Still another object of this invention is to provide asymmetrically shaped stabilizing planes for a hydrofoil craft wherein each stabilizing plane has a negative dihedral to provide early entrance into the water when the craft is forced to an excessive roll.

A still further object of this invention is to provide asymmetrically shaped stabilizing planes for a hydrofoil craft wherein the planes are arranged to have a high angle of attack relative to the surface of the water whereby a maximum lifting force is obtained which tends to add an additional counteracting force to further correct an excessive roll.

Another object of the invention is to provide relatively thick stabilizing planes for a hydrofoil craft which will also serve as protective fendersfor vulnerable sections of the submerged foil appendages.

Further and more detailed objects and advantages of this invention will appear from the following description and the accompanying drawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of the hydrofoil craft equipped with the stabilizing means which is the subject of this invention.

FIG. 2 is a side elevational view of a section of the hydrofoil craft showing the high angle of attack of the stabilizing planes.

FIG. 3 is a rear elevational view of the hydrofoil craft showing the negative dihedral in the stabilizing planes.

Referring now to the drawings wherein like reference numerals designate like or corresponding parts throughout the several views, there is shown in FIG. 1 a hull 10 having forward foil appendages 12 and rear foil appendages 14. It will be realized however, that the type of craft described is chosen for illustrative purposes only and that the invention could be prac' ticed on other types of hydrofoil hulls.

Propulsion for the hydrofoil craft is obtained in the hullborne position by a power driven propeller 16. The waterline of the hydrofoil craft in the hull-borne position is designated as H.W.L. in the drawings. When the craft is in a foil-borne position the waterline would be located approximately at F.W.L. as shown in FIG. 2.

Propulsion for the hydrofoil craft in the foil-borne position is by power driven propellers 18. Although the propulsion means shown employs propellers of conventional design, it will be realized that other types of propulsion, water jet for example, may be utilized without departing from the spirit of the invention.

Stabilizing planes 20 and 22, as shown in FIG. 3, are located on opposite sides of the hydrofoil craft above the hull-borne waterline H.W.L. It is generally desirable, as a secondary function, to employ the planes as protective fenders for the submerged foils l4 and hence the planes designed to be relatively thick and are positioned directly above the foils as indicated in FIG. 2. A more favorable location for the plane, however, would be forward of the center of gravity of the hydrofoil craft since both roll and pitch lifting and correcting moments would therefore be possible.

The specific placement of the stabilizing planes is not absolutely critical since the function of the planes in correcting the excessive roll in a watercraft will be accomplished by the planes in either of the aforementioned positions. Moreover, the correcting function is not particularly diminished by locating the planes at other positions on the hull than forward of the center of gravity of the craft or immediately above the rear foil appendages.

it should be observed, however, that as the position of the stabilizing planes is moved from the location shown in FIG. 2 to a more forward position toward the bow of the craft, the angle of attack of the plane should be increased in order to develop a greater lifting moment. This increase in the lifting moment will serve to prevent the bow of the craft from diving under the water. Here again, it should be realized that the inciusion of an angle of attack a as shown in FIG. 2 other than zero, merely refines the overall purpose of the invention. The principal factor in preventing the loss of a hydrofoil craft due to an excessive roll is the addition of the stabilizing planes 20 and 22, which, per se, produces new, novel, and -unobvious results in the operation of such watercraft.

Referring to FIG. 3, the stabilizing planes 20 and 22 are shown to be inclined downwardly at an angle [3 toward the waterline H.W.L. of the craft. The planes in this downward position are generally termed to have anegative dihedral.

In a situation whereby the hydrofoil craft is forced into an excessive roll, the negative dihedral of the planes 20 and 22 will enable the planes to engage the water at the beginning of the roll to thereby develop early recovery moments.

For purposes of illustration, the stabilizing planes have been shown in the drawings in the shape of a conventional air-foil so that drag on the stabilizing planes is reduced to a minimum. However, it will be realized that other shapes may be included without departing from the spirit of the invention.

The objects and advantages of the present invention have been fully and effectively accomplished by the stabilizing planes described above and illustrated in the drawings. Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described.

l claim:

1. A hydrofoil craft auxiliary stabilization means comprising:

a hull member; I

longitudinally spaced hydrofoils operably connected to said hull and extending in spaced relation to the bottom of said hull; and

fixed stabilizing planes attached to and extending outwardly from said hull having a negative dihedral and a high angle of attack with respect to a line parallel to a baseline of said hull positioned on said hull above a hull-home waterline for stabilizing said craft in case of adverse operating conditions when said conditions cause the stabilization planes to enter the water. 

1. A hydrofoil craft auxiliary stabilization means comprising: a hull member; longitudinally spaced hydrofoils operably connected to said hull and extending in spaced relation to the bottom of said hull; and fixed stabilizing planes attached to and extending outwardly from said hull having a negative dihedral and a high angle of attack with respect to a line parallel to a baseline of said hull positioned on said hull above a hull-borne waterline for stabilizing said craft in case of adverse operating conditions when said conditions cause the stabilization planes to enter the water. 